SOURCE: Except as noted, number of vessels-U.S. Army Corps of Engineers,
Institute for Water Resources, Waterborne Transportation Lines of the United
States: Calendar Year 2000 (Fort Belvoir, VA: 2001), also available at http://www.iwr.usace.army.mil/ndc/veslchar.htm,
vol. 1, table 1, as of April 2001; ton-miles-U.S. Army Corps of Engineers,
Institute for Water Resources, Waterborne Commerce of the United States (Washington,
DC: 2001), Part 5, table 1-4.